This application claims the priority of Korean Patent Application No. 2003-17979, filed on Mar. 22, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to encoding and decoding of digital data, and more particularly, to a method and apparatus for encoding and decoding bit rate scalable digital data.
2. Description of the Related Art
As digital signal processing technologies advance, audio signals are mostly stored and played back as digital data. Digital audio storage and/or playback devices sample and quantize analog audio signals, transform the analog audio signals into pulse code modulation (PCM) audio data, which is a digital signal, and store the PCM audio data in an information storage medium such as a compact disc (CD), a digital versatile disc (DVD), or the like, so that a user can play back data from the information storage medium when he/she desires to listen to the PCM audio data. Digital audio signal storage and/or reproduction methods considerably improve sound quality and remarkably reduce the deterioration of sound caused by long storage periods compared to analog audio signal storage and/or reproduction methods used on a long-play (LP) record, a magnetic tape, or the like. However, the large amount of digital data sometimes poses a problem for storage and transmission.
In order to solve these problems, a wide variety of compression technologies for reducing the amount of digital audio data are used. Moving Picture Expert Group audio standards drafted by the International Standard Organization (ISO) or AC-2/AC-3 technologies developed by Dolby adopt a method of reducing the amount of data using a psychoacoustic model, which results in an effective reduction in the amount of data regardless of the characteristics of signals. In other words, MPEG audio standards and AC-2/AC-3 technologies provide almost the same sound quality as a CD only at a bit rate of 64 Kbps–384 Kbps, that is, at ⅙–⅛ that of existing digital encoding technologies.
However, all these technologies comply with a method of detecting, quantizing, and encoding digital data in an optimum state at a fixed bit rate. Thus, when digital data is transmitted via a network, transmission bandwidth may be reduced due to poor network conditions. Also, the network may be disconnected, such that network service is not available. Also, when digital data is transformed into a smaller bitstream so as to be suitable for mobile devices having a limited storage capacity, re-encoding should be performed to reduce the amount of data. To achieve this, a considerable amount of calculation is required.
For this reason, the present applicant filed an application for “Digital Encoding and/or Decoding Method and Apparatus Using Bit-Sliced Encoding Technology” as Korean Patent Application No. 97-61299 on Nov. 19, 1997 in the Korean Intellectual Property Office and has been granted Korean Patent Registration No. 338801 on May 18, 2002. According to bit-sliced encoding technology, a bitstream, which has been encoded at a high bit rate, can be transformed into a bitstream having a low bit rate. Since reconstructing can be achieved using only a portion of a bitstream, even if a network is overloaded, the performance of a decoder is poor, or a user demands a low bit rate, the user can be provided with service at moderate sound quality using only a portion of the bitstream (though the performance of the decoder may deteriorate as much as low bit rate).
However, according to the bit-sliced encoding technology, all binary data mapped into bit planes is encoded. Thus, if more than half of the bit planes is values of “0”, the values of “0” are all encoded, which may reduce an encoding efficiency.